§ 5-301. Certain employment contracts void. Every undertaking or
promise, whether written or oral, express or implied, constituting or
contained, in any contract or agreement of hiring or employment between
any individual, firm, company, association or corporation and any
employee or prospective employee of the same, whereby (a) any employee
or prospective employee undertakes or promises to join, become or remain
a member of a company union; or (b) either party to such contract or
agreement undertakes or promises not to join, become, or remain a member
of any labor organization or any organization of employers; or (c)
either party to such contract or agreement undertakes or promises that
he will withdraw from the employment relation in the event that he
joins, becomes or remains a member of any labor organization or of any
organization of employers, is hereby declared to be contrary to public
policy and wholly void and shall not afford any basis for the granting
of legal or equitable relief by any court against a party to such
undertaking or promise, or against any other persons who may advise,
urge or induce, without fraud, violence, or threat thereof, either party
thereto to act in disregard of such undertaking or promise.